The split between mining power is irrelevant, what ever fork the exchanges and merchants accept IS Bitcoin and the other fork is worthless, without the exchange and merchants to complete the circle BTC doesn't have any value regardless of the hash rates involved.
No, no, no. Bitcoin is a set of rules, a "protocol", if you'd prefer that word. If there is a fork, the branch that does not follow the current rules is "not-bitcoin", and "bitcoin" continues as usual. It doesn't matter what the looters call their branch, it will be "not-bitcoin", even if not in name.